The invention is based on a method for improving the wanted signal in a radio receiving unit.
It is known for a signal-strength detection unit to be used to detect the ratio of the input signal to the wanted signal obtained after it. A disadvantage in this case is that interference elements, which are also amplified, not only corrupt the output signal of the signal-strength detection unit, but can also adversely affect the quality of the wanted signal.
The invention is based on the object of providing a method for improving the wanted signal in a radio receiving unit. This object is achieved by the features of the invention specified in claim 1. Advantageous developments of the invention are specified in the dependent claims.
The method according to the invention for improving the wanted signal in a radio receiving unit having a channel filter, having a switch, having a control unit, having a signal-strength detection unit and having controllable amplifiers is distinguished in that the control unit drives the switch in such a manner that the switch alternately supplies a first signal upstream of the channel filter and a second signal downstream of the channel filter to the signal-strength detection unit, and that the output signal of the signal-strength detection unit, also referred to as the detector signal, is supplied to the control unit, and that the amplifiers are driven as a function of the two values of output signal.
There is a direct relationship between the output voltage and the wanted signal, which is intended to be improved. If the output signal is improved, the wanted signal is also improved. If the output voltage deteriorates, the wanted signal deteriorates.
By supplying the respective first and second signal to the signal-strength detection unit, and the comparison which is carried out with the aid of the control unit, the amplifiers are driven in such a manner that an improved wanted signal is obtained by using the method according to the invention.
The method is furthermore distinguished in that the first signal contains a wanted signal element and an interference signal element, and in that the interference signal element is filtered out by the channel filter.
Elimination of the interference signals by using the channel filter allows the signal strengths to be evaluated with or without an interference signal.
The method is also distinguished in that the first signal, upstream of the channel filter, is amplified by a first amplifier, and the second signal, downstream from the channel filter, is amplified by a second amplifier.
By using the amplifiers to amplify the respective signals, it is possible to carry out an optimization as a function of how the two detector signals turn out. The optimization is in this case carried out fully automatically by the control unit.
The method is also characterized in that the gain setting is optimized such that the ratio N/(S+R) of the wanted signal N to the interference signals S and the noise R is as high as possible.
Normally, the unit operates with high gain in the first amplifier, in order to keep receiver noise low. However, by means of the method according to the invention, it can be stated that, when the gain in the first amplifier is high and powerful interference signals are present, only a low ratio N/(S+R) is in consequence achieved. An improved output signal can be obtained if the gain of the first amplifier is reduced, and the gain of the second amplifier is increased.
The method is furthermore distinguished in that, if it is found by the control unit that the wanted signal is greater than the interference signals, maximum gain is set in the first amplifier, and a reduced gain is set in the second amplifier.
The method is also distinguished in that, if the ratio N/(S+R) of the output signal is low when the gain of the first amplifier is at a minimum and severe interference sources are present, the frequency range is changed.
If the output signal is still poor even with low gain in the first amplifier, the channel is changed in order in this way to improve the output signal by raising the wanted signal level in comparison with the interference source.
Instead of the switches which supply the different signals to the signal-strength detection unit, it is also possible to use two signal-strength detection units, which continuously supply both signals to the control unit.